Processing · edge quality
Cutting plastic cores: saw, crush knife or lathe?
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The three cutting methods
Circular saw. A toothed blade passes through the tube and removes a strip of material as wide as the teeth, usually 1–3 mm. It cuts any wall and leaves a square edge. It produces chips and, on plastic, sometimes internal burrs that must be removed.
Crush knife (rotary knife). The tube turns on a mandrel and a plain disc blade moves in and parts it by pressure. It removes no material and makes no dust: that is why it is the most common solution for cardboard. On rigid plastic it can chip the edge; on soft plastic it can squash it and leave a lip.
Lathe (parting off). The tube turns and a fixed, narrow-pointed tool cuts it, as on a metal lathe. It gives the best squareness and a smooth face, and can chamfer the inside or outside diameter in the same pass. It is slower and costs more.
Which cut for which plastic
Fiaptech technical documentation (a company with corporate ties to ROLL) gives cut quality scores from 1 to 5 by material and method:
| Method | PVC | PP | PE | Dust |
|---|---|---|---|---|
| Saw | 5 | 3 | 3 | high |
| Crush knife | 1 | 2 | 2 | low |
| Lathe | 2 | 5 | 5 | medium |
The logic is physical. Rigid PVC is hard and chips under a blade that pushes, but it is removed cleanly by the teeth of a saw. PP and PE are tough and semi-crystalline: with a saw, friction heat softens them and they leave strings, while a lathe tool cuts them with a continuous chip and a clean face. These are one manufacturer’s assessments: some machines with dedicated blades and suitable settings also cut plastic well by pressure. Before choosing, ask for a cutting trial on your own tubes.
General tips for plastic:
- moderate cutting speeds, so the edge does not melt;
- a support mandrel matching the tube’s inside diameter;
- sharp tools: a worn blade heats and tears;
- chip extraction, because chips pick up static and stick everywhere;
- an internal chamfer for cores that go onto shafts with little play.
Tolerances and how to measure them
Core cutter manufacturers usually claim length precision between ±0.1 and ±0.3 mm for automatic machines; on manual machines precision depends on the operator. Checking these tolerances needs a suitable instrument: a tape measure reads 1 mm and is not enough. Use calipers or measuring stops.
Squareness of the cut is measured as the deviation in millimetres of the face against a square resting on the tube. It matters for the gaps between cores side by side on the shaft and for how plugs and end walls sit. Asking for tighter tolerances than necessary raises the cost with no benefit.
Typical defects and remedies
| Defect | Probable cause | Remedy |
|---|---|---|
| Chipped edge (PVC) | crush knife, cold, worn tool | fine-toothed saw; tube at room temperature |
| Strings and burrs (PP, PE) | friction heat, saw | lathe; lower speed; deburring |
| Inward lip | crush knife with fast feed | slower feed; support mandrel |
| Melted or glossy edge | excessive speed | reduce speed; sharp tool |
| Out-of-square face | insufficient clamping, flexing tool | better clamping, check with a square |
| Chips inside the core | no extraction | extraction, blowing, ionisation |
Deburring and chamfering
After cutting, a plastic core may have burrs on the inner edge, on the face or on the outer edge. Inner burrs catch on shaft lugs or chuck cones; outer burrs scratch the material of the first wraps. A light chamfer on the inside diameter makes it easier to slide onto the shaft and reduces the risk of chipping during fitting, especially for cores that are reused many times. On a lathe, chamfering happens in the same pass as the cut; after a saw, a separate deburring step is needed.
Cut in-house or buy ready cut
Buying cores already cut to length is the simplest choice with few lengths and large volumes. Cutting in-house from long tubes pays when lengths change often, when quick deliveries are needed, or when returned cores are trimmed for reuse. In that case, choose a machine suited to the plastic you use most, and plan for deburring. Returned cores are trimmed by removing damaged ends: the usable length shrinks with each cycle.
Safety
The main hazards are cutting and entanglement (rotating blade and mandrel), flying chips and saw noise. Basic measures: interlocked guards, emergency stop, tube presence sensors, tool changes with the machine stopped and locked out. New machines in the EU must comply with Machinery Regulation (EU) 2023/1230, applicable from 20 January 2027; in Great Britain the Supply of Machinery (Safety) Regulations 2008 apply, with UKCA or CE marking. When buying a used machine, the marking, the declaration of conformity and the condition of the guards all count.
Frequently asked questions
How are PVC cores cut?
Normally with a fine-toothed circular saw, which gives the cleanest edge on rigid PVC. A crush knife tends to chip it. Extract the chips and, if needed, deburr the inner edge.
How are PP and PE cores cut?
The best result comes from a lathe: a clean, square edge and the option to chamfer. With a saw, PP and PE tend to leave strings because of friction heat.
Can the same core cutter cut cardboard and plastic?
Many machines can, with the same tool or a quick change, but the quality on plastic depends on method and settings. Run a cutting trial on your own tubes before choosing.
What length tolerance can be achieved?
Automatic machines usually claim ±0.1–0.3 mm. Checking it needs a caliper or a gauge stop: a tape measure, with 1 mm resolution, is not enough.
Further reading
PVC cores
Rigid PVC cores, virgin or recycled: stiffness, weight, temperature, reuse, cutting, food contact, separate recycling and PPWR. With data, ratios and sources.
PP cores
Plain and CaCO₃-filled polypropylene cores: low weight, temperature, creep, cold, UV, food contact, steam sterilisation, lathe cutting and recycling.
Sizes and tolerances
Plastic core sizes: diameters in inches and mm, walls, ISO 13542 tolerances, ovality, TIR, smooth or ribbed bore, shafts and how to measure cores properly.
Reuse
Reusable plastic cores: how many cycles, how to organise returns, inspection, washing, traceability, cost per use and the PPWR rules on reusable packaging.
Hygiene and food
Plastic cores for food, pharmaceutical and cleanroom film: no fibres, washing, Regs 1935/2004 and 10/2011, GMP, NIAS, recyclate, FDA and returned cores.
Sources
- Fiaptech technical documentation, Smart Book “Which core?”, section “How can you cut it?” (a company with corporate ties to ROLL)
- ISO 11093-9 (specimen preparation, cut at 90° ± 1°)
- Regulation (EU) 2023/1230 on machinery, EU-OSHA
- Supply of Machinery (Safety) Regulations 2008 (Great Britain), Health and Safety Executive
- EN ISO 12100, general principles for design and risk assessment
- Cutting precision claimed by core cutter manufacturers (ROLL Lab research, 2026)
- ROLL Lab analysis (defects and remedies table)
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